Printing a pdf is sometimes a bit tricky. Here are some useful tips:
BEFORE PRINTING CARDS (or other pdf's where size matters):
  
To make sure they print correctly, when you push the print button in  adobe and the print box pops up with a small preview of the pdf on the  right, look to the left side where it says page scaling with a drop down menu next to it. Make sure "none"  is selected in the drop down menu. This should keep the cards centered. I also  recommend printing them on white cardstock. Then simply cut them in  half to make them 5.5 by 8.5 inches and fold them in half. They will fit  perfectly in an A2 size envelope which you can purchase at any  stationary store, and most office supply stores.
 
 
